Material Based on Distance from Origin
Considering your mesh vertices are approximately centered around the object origin (if not, this will not work as expected with this solution), you can use this kind of setting:

From the object output of texture coordinate (which gives x,y,z values relative to the origin).

Calculate the distance to the center (dot product then square root).

Subtract some value which may correspond to the inner orange part distance to the origin.

Input this result into a colorramp tuned to mix yellow/orange appropriately.